Automatic plumb and level tool with acoustic measuring capability

ABSTRACT

An automatic plumb, level, pointing and distance measuring tool uses a visible laser diode to project a beam in any of several different modes through a beam exit window. The tool, approximately the size and shape of a tape measure, can be placed on one edge to project a tilt-compensated vertical beam. Placed on another edge 90°-rotated, the tool projects through the same exit window a tilt-compensated horizontal beam. When laid on either of its larger flat sides, the tilt compensation becomes inoperative and the tool projects a beam which is fixed relative to the housing. Acoustic distance measurement is facilitated using a second component or target side device which is activated to send an acoustic signal across a space to be measured, toward the laser tool. A receiver in the laser tool detects arrival of the acoustic signal and causes the laser to project a characteristically modulated or pulsed beam, received at a photodetector on the target side device. The acoustic transit time is clocked and distance is calculated and displayed. The use of a single acoustic transit time, without reflection increases distance measuring range. Also, the visible laser beam projected between the two components provides a clear visual indication of the distance to be measured.

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.602,353, filed Oct. 22, 1990, now U.S. Pat. No. 5,075,977.

BACKGROUND OF THE INVENTION

This invention relates to hand tools, and in particular the invention isconcerned with a compact hand tool, generally in the size and shape of atape measure, for projecting a laser beam for use in relatively preciseplumbing and leveling operations. The device has a further use ofprojecting a pointing beam for use in alignment or layout.

A variety of survey and carpentry tools have previously employed lasers.For example, see U.S. Pat. Nos. 3,897,637, 3,771,876, 4,221,483,4,679,937, 4,781,457, 4,852,265 and 4,912,851.

In U.S. Pat. No. 3,897,637, there is disclosed a level and squaring toolutilizing a helium-neon laser for projecting a beam both vertically andhorizontally. The device was not self-leveling and required manualleveling. It was rather large and required connection to an externalsource of power.

U.S. Pat. No. 3,771,876 was directed to a laser apparatus for producinga plane or conical optical reference surface. The device used a pendulumhanging from a flexible suspending member, with the pendulum containingthe light source so as to be self-leveling. A double mirror or prismdevice was used for reflecting the beam out of the device 90 degreesfrom the entry angle of the beam from the pendulum. The double mirror(sometimes called a pentaprism) device was fixed in the unit and allowedfor changes in the angle of the approach of the light beam from thependulum.

Rando U.S. Pat. No. 4,221,483, assigned to the assignee of the presentinvention, discloses a laser beam level instrument using the principleof translation of a lens which collimates a laser diode beam in order tocompensate for small degrees of tilt in the instrument. The collimatinglens is suspended as a pendulum and has the effect of maintaining thecollimated beam in a truly vertical position providing self-leveling ina limited range of movement of the instrument.

U.S. Pat. No. 4,679,937, also assigned to the same assignee as thepresent invention, discloses a self-leveling battery-powered surveyingtool. The tool, which is designed to be set up on a tripod, provides areference for leveling and alignment. The apparatus, which includes alaser diode as a light source for projecting a generally horizontal butnon-planar cone of light from a reflecting cone, includes a tiltcompensation arrangement relevant to the present invention. Thereflecting cone is suspended by a wire having a controlled stiffnesswhich allows the mirror cone to tip at an angle which is one-half theangle of tilt error of the instrument from true plumb.

A contractor's tool for referencing a chosen elevation at a buildingsite was marketed in the 1970s as Model 840 Building Laser, by theassignee of the present invention. The product also was capable ofemitting a vertical beam. It had a helium-neon laser and was powered byan internal battery. The device was not self-leveling.

U.S. Pat. Nos. 4,852,265 and 4,912,851, also commonly owned with thepresent invention, disclosed level, plumb and alignment tools utilizinga laser diode and having tilt compensation means for small tiltvariations from levelness of the housing. The device compensated fortilt in either of two directions of variation from true horizontal ofthe housing, such as when the tool was placed on a non-level section offloor. It was stated that the device compensated for tilt errors of upto about five degrees, while still projecting a beam from the tool insubstantially true vertical or substantially true horizontalorientation.

In order to achieve the ability to project either a truly vertical orhorizontal beam, the level/plumb tool of the latter two patents utilizeda single pendulum-type tilt compensator in a preferred embodiment, withswitching of the output beam's orientation achieved by rotating a dialwheel through 90°. The rotation of the dial wheel moved a two-mirrorright angle deflector onto the path of a tilt-compensated vertical beam,deflecting it to horizontal. The housing itself, which in a preferredembodiment was somewhat like a level in shape, remained in the sameorientation for both horizontal projection and vertical projection.

While the latter two patents referenced above disclosed an effectivelevel, plumb and alignment tool, none of the previous devices was ascompact, as versatile in operation, as easily transported and as ruggedas the plumb, level and pointing beam device of the present invention asdescribed below.

SUMMARY OF THE INVENTION

The present invention achieves these objectives in a small, compact toolwhich may be about the size, shape and feel of a tape measure. The toolis simpler in operation than those described above, in having a singlebeam exit window in a preferred embodiment. An internal tiltcompensation means is effective to achieve substantially true verticalorientation of the emerging beam when the housing rests on one side oredge, and substantially true horizontal beam orientation when thehousing is moved to rest on another side or edge which is at rightangles to the first. In a preferred embodiment, two different tiltcompensation devices are included inside the housing, a first forcorrecting for tilt when a vertical beam is to be projected and a secondfor correcting for tilt when a horizontal beam is to be projected.

The two tilt compensation devices may comprise a weighted pendulum withan obliquely mounted mirror, for one orientation of the tool, and aweighted cantilever device having a second obliquely mounted mirror fora 90° rotated position. The second mirror interrupts the path of thebeam in this second position and compensates for tilt.

Further, the tool preferably includes means for fixing the position ofthe laser beam when the tool housing is rested on a third side, whichmay be a broader, larger flat surface of the housing, so that the beambecomes immobile relative to the tool housing without any tiltcompensation. In this mode, the tool is useful in projecting a beam forpointing or alignment purposes.

Any of a number of types of compensation means can be used in the tool,but the compensation means employed most preferably are those which aresimple, easily calibrated, reliable and providing a projected light beamwhose apparent origin is as close as possible to the bottom of theunit's housing, for minimization of parallax error.

In one specific embodiment of the invention, the compensation meanscomprise a weighted pendulum device for tilt compensation of thevertically projected beam; and a weighted cantilever device forcompensation of the horizontally projected beam. In one embodiment of avertical compensator, the pendulum-type tilt compensation device is atwo-axis pendulum which effects tilt compensation under the influence ofgravity for a first degree of mirror movement compensation generallywithin a plane including the beam incident and reflected from themirror; and for effecting a second, different degree of mirror movementcompensation in a generally transverse plane. This achieves accuratecompensation to true vertical beam orientation, regardless of thedirection (or combination of directions) in which the tool is tilted.The pendulum device, which may comprise a wire or rod of heavierdimension in one direction than the other, corrects for tilt of theinstrument essentially by permitting the mirror surface to change angleorientation by about 0.38 of the amount of tilt to which the unit issubjected. The compensation considerations are slightly different fortilt in the plane of the beam's incident and reflected from the mirrorversus tilt in a transverse plane. In the transverse plane slightly moremirror tilt correction is needed, since the laser diode beam approachesthe mirror from an oblique angle.

In another embodiment a simple, symmetrical cross section round wire orrod is used for vertical compensation. The resulting transverse tilecompensation error is almost insignificant at short range.

Although the preferred embodiments of the invention as described hereinare believed to achieve the objectives of efficiency in construction anduse, as well as ruggedness, dependability and compactness, other typesof tilt compensation can be employed. Other methods and devices forproducing a plumb beam include a pendulous lens as in U.S. Pat. No.4,221,483; a pendulous laser assembly as in U.S. Pat. No. 3,771,876; apendulous prism as in U.S. Pat. No. 4,781,457; and a pendulous window asin German Patent No. 2,944,408. These systems are believed generallymore costly, but could be made to work with a horizontal compensatorwhich intercepts the beam before the beam arrives at the verticalcompensator.

An important objective achieved by the present invention is simplicityin use of a level, plumb and pointing device. Instead of rotating amechanical dial on the exterior of the device as described in thereferenced U.S. Pat. Nos. 4,852,265 and 4,912,851, the compact, tapemeasure-sized tool is simply placed on a surface with the beam exitwindow either in vertical orientation or in horizontal orientation. Tiltcompensation, as well as selection of the proper tilt compensator (forvertical or horizontal) is achieved automatically by the particularcompensation means employed.

Further, as noted above, when the device is to be used for a fixedgenerally horizontal pointing beam or reference beam, it is simply laidon a third side, i.e. a larger flat side (it can be laid on either broadside in a preferred embodiment). This fixes the position of a tiltcompensator relative to the laser beam, and stabilizes the beam withrespect to the tool housing.

Accordingly, in one preferred embodiment a portable laser beamprojecting device for indicating level, plumb and alignment inaccordance with the invention includes a hand-carryable housing havingat least two sides capable of resting stably on a flat surface, with thetwo sides being substantially perpendicular to each other. These arepreferably two of the narrower edges of the housing. A laser means ismounted within the housing, for producing at least one collimated beamof visible laser light. A beam exit window is positioned in the housingfor outward projection of the beam. Beam directing means in the housingare effective to direct a beam from the laser source means verticallyout of the housing through the exit window when a first side of said twosides is held generally horizontal, and for directing a beam from thelaser source means horizontally out of the housing through the exitwindow when a second side of said two sides is held generallyhorizontal. Tilt compensation means in the housing, and associated withthe beam directing means, correct for relatively small tilt angles ofthe housing as it rests with one of the two sides against surfaces nottruly horizontal or not truly vertical. The tilt compensation meansproject the beam through the exit window in substantially true verticalorientation or substantially true horizontal orientation despite suchrelatively small tilt angles.

In one specific embodiment, the laser source means may comprise twoseparate laser diodes, one for vertical beam projection and one forhorizontal. Thus a diode/lens assembly is provided for each tiltcompensator. An appropriate form of switch is included, to activateeither the horizontal diode beam or the vertical diode beam (or twobeams can be projected simultaneously if desired). In a preferredembodiment of such a two-diode device, the housing still includes onlyone exit window, and a mercury switch can be used to select between thetwo diodes. When the housing is moved to a position for vertical beamprojection, a first diode is switched on and is tilt-compensated using afirst tilt compensation device. When the housing is moved to a positionfor horizontal beam projection, the second diode is energized to projecta different beam, reflecting off a different tilt compensator effectiveto correct for tilt in this second orientation.

Alternatively, a two-laser diode/two lens embodiment of the inventioncan have the two diodes themselves tilt compensated, rather than usingtilt compensation mirrors.

An additional important feature of the invention is damping of themovement of tilt compensators, so as to stabilize the projected beam inthe substantially true vertical or true horizontal orientation asquickly as possible after the housing is set in position. This may beachieved by liquid damping, wherein two different tilt compensators, onefor vertical and one for horizontal, are encased in a liquid. The laserdiode beam enters the liquid and is reflected from one of the twocompensators inside the liquid being redirected toward the exit window.Indices of refraction of the damping liquid and of any glass interfacethrough which the beam passes are taken into account in this type ofdamping.

As alternatives, the device can employ air damping or magnetic damping,as described in the above referenced U.S. Pat. Nos. 4,852,265 and4,912,851. The disclosures of those patents are incorporated herein byreference.

It is therefore a primary object of the present invention to provide asimple, very compact and easily used hand tool for projecting a plumb orhorizontal laser beam, or a pointing laser beam, with substantially truevertical and horizontal orientations achieved regardless of relativelysmall tilt angles of the housing as it is held or as it rests on anon-horizontal surface. A principal purpose of the invention is toprovide such a tool which employs gravity to switch from one type ofcompensation to the other, as the housing is reoriented from verticalprojection to horizontal, or vice versa. Further, gravity may be used toswitch from either of the compensated vertical or horizontal laser beamsto a fixed pointer beam, by de-activating the tilt compensators andfixing at least one of them when the housing is laid on a third side.These and other objects, advantages and features of the invention willbe apparent from the following description of preferred embodiments,considered along with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a plumb, level and pointing tool inaccordance with the invention, with the device used to project a beamvertically.

FIG. 2 is a similar perspective view, showing the tool of the inventionused in another mode, with the device used to project a horizontal beam.

FIG. 3 is a further perspective view, showing the tool used in a furthermode, to project a pointing beam.

FIG. 4 is an elevation view in section, showing the construction of thetool in one preferred embodiment, with a first tilt compensation forvertical beam projection and a second tilt compensation (inactive) forhorizontal beam projection. The tool is shown in position for use as aplumbing or vertical alignment tool, as in FIG. 1.

FIG. 5 is an elevational section view similar to

FIG. 4, but showing the tool in a 90°-rotated position, for use inprojecting a tilt-compensated horizontal beam, as in FIG. 2.

FIG. 6 is a schematic view in elevation showing a two laser/lensembodiment of the invention.

FIG. 7 is an exploded perspective view showing a preferred embodiment ofa vertical plumb compensator in accordance with the invention.

FIG. 8 is a partial elevation view, somewhat diagrammatic, showing theoperation of the horizontal tilt compensator in one embodiment of theinvention.

FIG. 9 is an exploded perspective view showing a portion of thehorizontal compensator.

FIG. 10 is an exploded perspective view further illustrating principlesof a tilt compensator in accordance with the invention. The figure showsa gravity activated brake for use in the pointing mode as shown in FIG.3.

FIG. 11 is a view illustrating one aspect of the apparatus and methodillustrated in FIG. 10.

FIG. 12 is a schematic view showing the effect of different angles ofemergence from a liquid damping medium of the tool.

FIGS. 13A, 13B, 13C and 13D are companion perspective views illustratinganother embodiment of the invention, wherein a tape measure is includedas part of the tool.

FIGS. 14 and 15 are perspective views showing further embodiments of theinvention, wherein a tape measure is integrated with the level/plumbindicator.

FIG. 16 is a schematic sectional view showing a device for projection oftilt compensated beams in both up and down vertical directions.

FIG. 17 is a schematic drawing in block diagram form, showing a deviceaccording to the invention wherein an acoustic measuring device includesa laser or other light source for triggering a time clock to read adistance via an acoustic signal.

FIG. 18 is a view showing one embodiment of a physical configuration fora target device which forms a component of the apparatus shown in FIG.17.

FIG. 19 is a perspective view showing a laser plumb/level tool such asin FIGS. 1-6, but incorporating acoustic measuring features as describedrelative to FIG. 17.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the drawings, FIGS. 1, 2 and 3 show a plumb, level and alignment tool10 as used in successive positions of projecting a vertical plumb laserbeam 12v when resting on a first side or edge 14 (FIG. 1), a horizontalbeam 12h when resting on a second side or edge 16 (FIG. 2), and agenerally horizontal pointing beam 12p when resting on another side,i.e. a broad, flat side 18 (FIG. 3).

The tool 10 has a housing 20 which is generally in the shape and size ofa tape measure (e.g. a 25-foot pocket tape measure). It preferably has alength or height along each of the edge surfaces 14 and 16 of about 4inches or less, and more preferably less than 33/4 inches. The thicknessof the tool housing preferably is less than about 2 inches, and in apreferred embodiment may be less than 11/4 inches.

The sides or edge surfaces 14 and 16 must be capable of resting stablyon a horizontal surface (or against a vertical surface). To this end,they preferably are flat as shown, and at right angles to each other.However, these edges may instead be provided with embossings or feet toachieve stability on a surface, so long as some straight line visualindication is provided for the user, for giving the user a generalalignment indication for the tool.

FIGS. 1 and 2 show the inclusion on the housing of a notch 22 at theedge 14 and formed in a large flat side 24 of the housing; a line ornotch 26 in the side edge 16; and a notch 28 centrally disposed at theside edge 16 and adjacent to a beam exit window 30. These visualindicators, which can take any of a variety of forms, are provided toalign the tool 10 with reference lines or marks 32, 34 or 36 as seen inthe drawings. The visual alignment indicators give a reference for theprojected laser beam 12v or 12h, as illustrated. As seen and explainedfurther below, the tool 10 is provided with tilt compensation along twoaxes, particularly for the vertical beam projection mode shown in FIG.1, and the apparent source of the beam is controlled to remain as closeto the housing reference marks as possible. This is to reduce sine errorwhen the tool is at a significant tilt.

An external power switch 38 may be positioned on the outside of thehousing 20 as shown.

FIG. 4 shows the internal construction of the plumb, level and pointingtool 10 in one specific and preferred embodiment. The on/off switch 38,which may be a microslide switch as shown, is connected to a battery 40(e.g. a 9 volt battery) and to a visible laser diode 42 mounted insidethe housing. The diode mount 44 may be connected to stable structure 46in the housing by a tightened pivot mounting 48. A collimating(preferably temperature compensated) lens 50 can be precision adjustedin its distance from the diode 42 via a set screw 52 in this preferredembodiment.

Principal features of the invention, in this preferred embodiment, arethat the tool has a single beam exit window 30; that the user simplyselects a side edge 14 or 16 in order to choose between a verticallyprojected beam 12v and a horizontally projected beam 12h (FIG. 5); andthat the projected beam be compensated for tilt of the tool housing,still projecting a beam which is substantially true vertical or truehorizontal, whether the tool is held with the edge 14 generallyhorizontal or the edge 16 generally horizontal. This may be achieved invarious ways, as mentioned above. This preferred embodiment involves therelatively straightforward use of two alternate reflective surfaces fortilt compensation--one of which is operative when the beam is projectedvertically, and the other of which is operable when the beam isprojected horizontally.

FIG. 4 shows that a first reflector comprises a mirror 52 which isfixedly mounted on a pendulum weight 54, for vertical beam tiltcorrection. The pendulum weight is supported on a pendulum shaft or wire56, supported from a fixed position (pendulum mount) 58 in the housing.It has been found that in this vertical beam tilt compensation, thevertical correction can be quite accurate with a simple round rod orwire 56 is used as the pendulum shaft, with a symmetrical cross section.As explained in U.S. Pat. Nos. 4,852,265 and 4,912,851 incorporated byreference herein, for complete accuracy there must be a different degreeof tilt compensation for tilt along one axis as compared to tilt alongthe other axis, since the beam 12 from the diode/lens assemblyapproaches the compensation mirror 52 from an angle. However, it hasbeen found that if the pendulum rod 56 is of simple cross section and itis designed properly for tilt correction in the plane of the incidentand reflected laser beam (i.e. tilt within the plane of the paper inFIG. 4), tilt angles of the housing in the orthogonal direction (in andout of the page in FIG. 4) are still well within acceptable accuracy.For example, such a tilt of about 3° would produce an error of onlyabout 0.25 inch at 100 feet above the tool.

However, for ideal compensation for tilt with components in either orboth directions, the rod 56 may be made with an oblong, elliptical orrectangular cross section, for greater stiffness in the one directionthan in the other. The principles of such correction are explored andfully discussed in the patents incorporated by reference.

In the preferred embodiment illustrated, damping of the motion of thependulum weight 54 and mirror 52 following placement of the tool isachieved by liquid damping, although other suitable forms of damping maybe used. Thus, the housing includes a liquid such as a clear oil withina liquid enclosure space indicated at 60 in the drawing. The laser beam12 is shown passing through a glass (or other transparent material)sealing plate 62 which acts as an interface between the liquid space 60and the air space above. The beam 12 then passes down through thedamping liquid to the first tilt compensating mirror 52. As shown inFIG. 4, refraction occurs as the beam passes through the glass sealingplate 62 and again as the beam enters the damping liquid. The degree ofthis refraction depends on the index of refraction of the plate 62 andof the oil or other liquid. However, it is a fixed relationship, untilthe beam is reflected by a compensating mirror, and thus is a constant.

It should be understood that virtually the whole interior of thehousing, or the interior up to the exit window and to a point near thelens 50, can be filled with liquid if desired.

Although FIG. 4 shows the compensated vertical beam 12v exiting theliquid damping bath substantially at right angle to the plate 62, thiswill change with increasing tilt angles, and this effect is taken intoaccount. As will be seen later, and as illustrated in principle in FIG.12, the change in index of refraction multiplies the effect of positionadjustment in the compensating mirrors.

As an example in this preferred embodiment, if the tool 10 were to betilted at an angle of 2.8° within the plane of the incident andreflected laser beam (i.e. within the plane of the paper in FIG. 4), asimilar total correction of 2.8° must be made for the emerging plumbbeam 12v as compared to the orientation of the housing. In one preferredembodiment the pendulous mirror 52 and its connected structure will beset to tip one degree to make the correction. This correction is doubledto two degrees by the incidence and reflection of the beam on the mirror52. In addition, for a clear mineral oil damping bath with an index ofrefraction N of 1.4, this will increase the correction to 1.4×2°=2.8°,as the beam exits the liquid bath toward the exit window 30, enteringthe air. The effect of the beam's passing through the transparent plate62 at a slight angle is negligible in this situation.

FIG. 12 illustrates the relationship used in the equation above.

An increase in the viscosity of the oil or other liquid in the liquiddamping will increase the motion damping effect of the liquid, but atthe same time this can cause the device to compensate for tilt moreslowly. At the same time, an increase in viscosity generally correspondsto an increase in index of refraction, which will increase the beamemergence angle and thus require that the mirror 52 make a lower angleof deflection for a given tilt, for accurate compensation. These areimportant considerations in the selection of the damping liquid to beused in the tool 10.

FIG. 7 shows in exploded view some of the principal components of thevertical tilt compensation arrangement described with reference to FIG.4. As illustrated, the liquid damping bath may be contained in a tank 61such as of plastic. The tank 61, which is completely filled with liquid,may be sealed against the transparent plate 62 by an O-ring 61a, alsoseen in FIG. 4. A preferred feature of the tilt compensator is theinclusion of a caging device 63 for the pendulum's mirror support 54a(shown in somewhat different configuration from what is shown in FIG.4). The caging device 63 may comprise a notched plate as shown,positioned to straddle the pendulum weight or mirror support 54a in theassembled tool. The pendulum is straddled with sufficient clearance thatit can operate to adequately compensate for tilt in both orthogonaldirections discussed above. When the tool is laid on its side or carriedat a steeply oblique angle, the caging device 63 engages one of theedges of the pendulum device 54a and essentially immobilizes it, therebyprotecting it against damage and excessive movement which might bringabout eventual maladjustment.

Another important effect of the index of refraction of the liquid is inthe fixed portion of the beam's path as it leaves the diode/lensassembly 42, 50. The greater the index of refraction of the liquid, themore the laser beam will be bent as it enters the liquid, and thus thecloser to vertical the beam can be in the liquid, for a given offsetposition of the diode/lens. This lessens the incidence/reflection anglefrom the first tilt compensation mirror 52, therefore permitting themirror 52 to lie closer to horizontal. In turn, this will make tiltcorrection in the plane perpendicular to the plane of the light beam(i.e. in and out of the paper in FIG. 4) more accurate, assuming use ofa symmetrically cross sectioned pendulous support 56. In other words,ideal correction for tilt in the plane and transverse directions comesmore closely to requiring the same type of correction. (If the source ofthe beam could be from directly above the mirror 52, the tilt correctionproblem would be essentially identical in both directions).

In a preferred embodiment of the invention, the mirror 52 is at aninclination of about 17° off normal from the compensated vertical beam12v. Thus, as fully discussed in U.S. Pat. No. 4,912,851, for idealcorrection the stiffness of the pendulum rod 56 acting in the plane ofthe beam and of the paper in FIG. 4 would have to be somewhat greaterthan in the other direction.

The use of a liquid damping bath, preferably fairly viscous, has otherimportant advantages. The refraction effect allows a stiffer design ofthe tilt compensation devices. This, along with the fact that the liquidbath protects the movable members somewhat from jarring against thehousing, makes the tool far more rugged.

As seen in FIG. 4, a second tilt compensating reflective mirror 66,supported on a weight 68 at the end of a flexure component or cantileverbeam 70, is deflected out of the path of the laser beam 12 by theinfluence of gravity. When the tool 10 rests on the surface 14, or isheld with the edge surface 14 generally horizontal, themirror/cantilever weight assembly 66, 68, 70 is inactive. It is animportant feature, in this embodiment of the invention, that the meansfor switching from the first tilt compensation assembly 52, 54, 56 tothe second tilt compensation assembly 66, 68, 70 be responsive togravity, rather than requiring any mechanical switching, leveradjustment, etc. by the user.

FIG. 5 shows the tool 10 after it has been moved to a position whereinthe side or edge surface 16 is generally horizontal. The horizontal beamtilt compensator assembly is also detailed in FIGS. 8, 9, 10 and 11, andthose drawings should also be referred to, regarding the followingdiscussion.

In FIG. 5 the tool 10 is used to project a tilt-compensated horizontallaser beam 12h. Due to the influence of gravity, the cantilever weight68 of the second compensator has swung the cantilever beam 70 and thesecond mirror 66 down to a position of being directly in the path of thelaser beam 12 from the diode/lens assembly 42, 50. Thus, the secondcompensation mirror 56 interrupts the beam 12 before it reaches thefirst, vertical compensation assembly. The resulting correctedhorizontal beam 12h is projected out of the beam exit window 30 at aslightly different position from that of the vertical beam 12v in FIG.4.

As indicated in FIG. 5, the cantilever member 70 of the secondcompensator may be hanging generally vertically when it is interposed inthe path of the beam 12, as shown. However, this is not necessarily thecase and the cantilever member 70 could have a "normal" position whichis somewhat oblique. A counter weight 72 mounted on the cantileverweight 68 may be adjusted (via threaded connection) in order tocalibrate the tool and effect the accurate degree of horizontal tiltcompensation.

In this mode of the tool 10, the first, vertical tilt compensationassembly 52, 54, 56 is inactive as shown. The pendulum weight 54 mayrest against fixed structure 74 of the housing in this mode. In otherpositions it may be caged by the caging device 63 discussed above (FIG.7).

As shown in FIGS. 4 and 5, the cantilever beam member 70 of the secondcompensator is supported on a mounting bracket or other structure 76connected to the housing. There may also be, as shown in FIGS. 4, 5 and10, a brake weight 78 connected to the structure 76. As shown in theperspective exploded view of FIG. 10, this brake weight 78 may bepositioned in a central opening 80 of the cantilever member or beam 70,its purpose being to immobilize the cantilever beam 70 when the tool islaid on a broad side 18 as shown in FIG. 3 (or on the opposite broadside 24). Thus, when the tool is to be used as a pointing beam fordirecting a horizontal beam fixed relative to the housing, the brakeweight 78 flexes slightly as the tool is placed on either broad side,and lightly engages one of two cantilever beam arms 82, immobilizing thecantilever member 70 and mirror 66 relative to the housing. In thepointing beam mode, the first compensator assembly 52, 54, 56 is out ofthe path of the beam.

FIGS. 8, 9, 10 and 11 show further features of the horizontal toolcompensation assembly in a preferred embodiment of the invention. InFIG. 8 the counterweight 72 and its fine calibration adjustment on athreaded rod 86 are indicated. FIG. 9 is a further exploded view showingassembly.

FIGS. 10 and 11 illustrate an important feature of the horizontalcompensator which allows for a large range of linearity offorce/displacement in the system. That is, the tool is afforded aconsiderable degree of tilt, while the horizontal beam is still keptsubstantially truly horizontal. It has been found that the tilt angle ofthe tool as used in the horizontal mode shown in FIG. 5 can be plus orminus 7°, provided the cantilever beam 70 is designed properly. For atilt of plus or minus 7°, the device can achieve an accuracy within 20"of arc. (It is noted that the horizontal tilt compensator operates onlyin a single axis, since tilt rotation of the tool in and out of thepaper as seen in FIG. 5, even through an appreciable tilt angle, hasvirtually no effect on the horizontal accuracy of the beam.)

A preferred structure of the cantilever beam is shown in FIG. 11, whichshould be viewed along with FIGS. 8, 9, 10 and 5. The cantilever memberor beam 70 is formed of two legs 82 which are tapered. These taperedlegs become more and more flexible as their cross sections becomesmaller. If the center of gravity 84 of the cantilever weight 68 ispositioned at the point where the two sides of each tapering leg 82would intersect, the desired linearity of behavior of the beam 70 isachieved. This is because the moment and bending is distributed over thelength of the beam instead of being concentrated at one end. Thecantilever beam 70 could be a single tapered member, but the bifurcationof the legs 82 is preferred in this embodiment so that the brake weight78 can be fitted between them. Thus, an encircling rubber member 86 ofthe brake weight 78 can engage either cantilever leg 82, depending onwhich way the tool 10 is laid down.

FIG. 6 is a sectional view similar to FIGS. 4 and 5, but showing anembodiment of a laser plumb and level tool 90 having two separate laserdiodes/lens assemblies 42a/50a, 42b/50b. The arrangement shown in FIG. 6is only one example of the way in which such a dual laser source toolcan be constructed.

As shown in FIG. 6, in the particular embodiment illustrated separatebeam exit windows 92 and 94 are included, and the tool is thus used witha single side 14a generally horizontal, for projection of either of thebeams 12v or 12h, or the two beams simultaneously if desired.Alternatively, the tool can be constructed with a single beam exitwindow, with some of the optics and a second, horizontal tiltcompensation assembly 96 essentially mounted at right angles to what isshown. In such a single-window embodiment, the two beams could beprojectible through the single window at slightly offset positions fromone another. However, one advantage of the construction illustrated isthat the two beams 12v and 12h may be projected simultaneously ifdesired. Appropriate switching, in addition to the illustrated switch38, can be provided for this purpose.

In the tool 90 shown in FIG. 6, again a single liquid damping bath space98 can be provided. The structure and function of the second(horizontal) tilt compensation assembly 96, and of a first (vertical)tilt compensation assembly 99, along with many other constructionalfeatures, can be similar to what has been described earlier with respectto the tool 10.

FIGS. 13 through 15 show additional embodiments of the invention,wherein the plumb, level and pointing tool is integrated with a tapemeasure.

In FIGS. 13A through 13D, a plumb, level and pointing tool 10 such asdescribed above, secured by a pivot connection 100 to a tape measure 102of typical configuration. Both the tape measure 102 and the laser tool10 are shown in different positions of rotation and different positionsof relative rotation in these four drawings. In FIG. 13A the laser tool10 projects a tilt-compensated vertical beam 12v which may be used toreference the tool on an overhead beam or on a ceiling mark, forexample. Thus, a carpenter, plumber or other tradesman or worker can usethe tape 104 to measure a certain horizontal or generally horizontaldistance from the overhead mark at which the tool is located. The toolcan include markings indicating that the user should add a specifiedincrement, such as 1/2 inch, to the reading at the front 106 of the tapemeasure, to be corrected for the distance to the actual reference beam12v.

FIG. 13B shows the tape measure 102 rotated 90° from the position inFIG. 13A, and indicates that the tape 104 may be used to measure avertical distance with the tape 104 held truly plumb. Thetilt-compensated vertical beam 12v is used as a guide for accuratelyholding the tape 104 vertically.

In FIG. 13C the laser tool 10 has been rotated to a horizontal position,projecting a tilt-compensated horizontal beam 12h. Thus, the laser beamcan be used as a reference marking beam for accurate measurement along ahorizontal line using the tape 104.

In FIG. 13D, the tape measure 102 has been rotated to measurevertically, with the laser tool 10 still projecting a horizontal beam12h. This use of the tool is similar to that of FIG. 13A in that thelaser beam achieves an accurate reference from a distant point, i.e. itlocates the tool at a precise level, from which upward (or downward)measurements can be made to a specific point a given distance above (orbelow) the level of the horizontal beam 12h.

FIGS. 14 and 15 show further variations. In FIG. 14, a tape measure 106having arm brackets 108 can be snapped onto a modified laser tool 110,via openings in the brackets 108 and snap-like connections 112 on thelaser tool 110. As indicated, the beam window can be directly inside thesnap connection 112 shown in FIG. 14, so that the tilt compensatedvertical beam 12v is projected through this opening.

In FIG. 15 a tape measure 106 similar to that of FIG. 14 can similarlybe snapped onto a further modified laser tool 114. On the laser tool 114are four snap-like connectors 116, two on each opposing pair of narrowtool edges. In this way, the tape measure 106 can be selectivelypositioned in either of two right-angled positions to provideorientations relative to the laser beam 12 as needed. For example, thelaser tool 114 could be used in the vertical beam mode shown in FIG. 15,with the beam 12v located on an overhead point. Measurements could bemade in many different radial directions in a point thus located at thecenter of the tool 114, or a measured arc could be swung from such apoint. The tool can be used for similar purposes with the tape measure106 attached in the 90°-rotated position.

FIG. 16 schematically illustrates a variation of the invention wherein alaser tool 120 projects plumb beams 122a and 122b in both up and downdirections. As indicated, a pair of diode/lens assemblies 124a and 124bare included, projecting beams 124 in symmetrically opposite directions.The beams 124 can pass into a liquid damping bath as above, and thebeams are shown refracted due to such a liquid damping bath although thedamping bath is not specifically shown in this schematic view.

In this embodiment of the invention, the single pendulum tiltcompensator 126 can be included, with a pendulum weight 128, a pendulumsupport wire or rod 130 and a pair of compensating mirrors 132a and132b. It can be seen that, with the manner in which the mirrors aremounted and located (i.e. on the same side left/right of the weight128), a compensation of the upper beam 122a will effect an equalcompensation for the lower beam 122b, keeping them both substantiallytruly vertical. Such a tool has a number of uses in the fields ofcarpentry, mechanical contracting, electrical and plumbing. Points canbe located above and below a user, lying on the same vertical line.Studs, timbers and walls can be checked for plumb, without requiring theuser to bend down to the floor.

It should be understood that the laser tool of the invention can beintegrated with other tools. It can be integral with or attached to anacoustic distance measuring device, greatly aiding in accuracy of such adevice. The projected laser beam can serve as a pointing beam for thedistance measuring device, so that the device can be aimed at a specialacoustic reflector which may be placed on a wall whose distance from thedevice is to be measured. The pointing beam enables an accuracy indirectional orientation which would not otherwise be possible, and asmall reflective target can be used. Without such a pointing beam,acoustic distance measuring devices have tended to read the distance toa wood wall differently from the distance to a drywall, for example.

A further and more preferred embodiment of the above mentioned acousticdistance measuring device is shown in FIG. 17. In this embodiment, whichpreferably but not necessarily includes the plumb/level device, a lightbeam 140 is used to communicate the acoustic transit time. In this casethe acoustic pulse or wave form generator 142 is built into the targetdevice 144, as shown in the drawing. An acoustic signal indicated at 146is sent to a housing 148 containing the laser 150 and compensators (notshown). A microphone 151 built into the housing 148 detects the acousticsignal 146 and produces a signal processed by an amplifier/filter 152.The signal goes to a modulator 154, which modulates the outgoing lightbeam 140 via the drive current with a characteristic light signal,indicating receipt of the acoustic signal. A laser is indicated in thedrawing, but virtually any collimated light source which is modulatablecan be used.

In the device as described and shown in FIG. 17, the laser side deviceor housing 148 containing the laser (or other light source) acts as atransponder, being activated by the acoustic beam to emit the modulated,characteristic light signal in response. The laser side device 148 is"on" during the entire procedure, projecting a beam 140 so that thetarget device 144 can be properly located with the beam aimed at thephotodetector 158. The target device 144 is switched on (via a switch156) when the measurement is to be taken. Repeated measurementspreferably are taken (e.g. multiple repetitions per second) as long asthe target device is on, and the display will provide a series ofreadings, changing if the two components 144 and 148 are moved relativeto each other.

The target side 144 can, of course, be made to act as a transponder. Inthat case the characteristic light pulse would initiate the measurementsequence and would trigger the acoustic pulse from the driver 142. Aclock 160 and distance display 162 (shown in the target side 144) wouldthen be on the laser side, i.e. in the housing 148, and the calculationof distance would be performed and displayed in the housing 148.

The described device, system and method of measuring distance useone-way acoustic propagation, i.e. one acoustic transit time withoutreflection, and have several advantages over the conventional methods ofmeasuring distance using acoustics. First, there is an increase in rangebecause there are no reflection losses and a shorter acoustic path.Second, the interval of space being measured, between the laser side andthe target side, is clearly indicated visually to the user by thepreferably visible laser beam.

FIG. 18 shows one embodiment of a physical configuration for the targetdevice 144. The acoustic transducer/driver 142 may be located on a frontsurface of a face portion 164 of the target device, with thephotodetector 158 positioned nearby. The distance display 162 can belocated on a horizontal base portion 166, for example, as shown in FIG.18. The calculation of the distance via the clock and other associatedequipment (i.e. a microprocessor) will of course compensate for thelength of the base 166, if the back end of the base is abutted against avertical surface which is the subject of the measurement.

More preferably, there is provided an LCD 170 which has the capabilityof displaying pick marks 172 at every 1/16th inch (as an example) alongthe base 166, with numerical display of feet and inches (or metric, orselectively either). The numbers display in this embodiment preferablyis programmed to progressively "move" with respect to the base 166itself, if the target side device 144 is moved toward or away from thelaser side device 148. Thus, the numerical indications of feet andinches indicated in FIG. 18 will progressively move to the right or leftas the target device 144 is moved to left or right, respectively. Thenumerical indications therefore stay put relative to the laser sidedevice (not shown in FIG. 18), providing the user with a real-timeadaptive tool which gives the user a scale similar to a tape measure. Ifthe back end of the base 166 is pushed against a wall or other verticalsurface, the distance to that surface can actually be read using thescale.

Although the electronic circuitry for implementing the describedcalculation and display functions are not shown herein, they are wellwithin the skill of the ordinary engineer and LCD expert. Acousticmeasurement in itself is well known, as are the electronics to carry outan LCD display of an acoustic measurement.

In operation of the described embodiment, the measurement loop isinitiated on the target side. The on/off switch 156 is switched to the"on" position, activating a transducer 157 to cause the acoustic signalto be sent. When the signal has been received at the laser side devicethe light signal is sent. The photodetector 158 built into the targetdevice receives the optical signal (i.e. the laser beam or other lightbeam 140) and converts it to an electrical signal. In this case a clock160 starts at the time the acoustic signal 146 is sent, and stops at thetime the photo current from the photodetector 158 is measured. The timedifference between the acoustic pulse generation and the electricalsignal received from the photodetector is a measure of the distanceseparating the two instruments, with the included light beam transittime being negligible. This calculated distance may be displayed on thedistance display 162 in the target device housing 144, as indicatedschematically in FIG. 17.

If the target side is the transponder, then the sequence is started atthe laser side, as by a manual input which causes a pulse of light to besent.

The laser side device shown in FIG. 17, i.e. the housing 148, can beincorporated in and form a part of one of the embodiments of thelevelling/plumb tools described above. Thus, a level/plumb laserindicator device such as shown in FIGS. 1 through 5 or 6 can incorporatethe microphone receiver 151 and other components shown in the device148, so as to be capable of serving as the laser side device in theacoustic measuring apparatus. This provides a very versatile tool withcooperating uses in carpentry, heating and ventilating, plumbing andother layout endeavors.

FIG. 19 shows a modified laser projecting automatic plumb and level tool180, incorporated the acoustic distance measuring equipment as shown inthe laser side device 148 on the left side of FIG. 17, in accordancewith one preferred embodiment of the invention. The combined tool 180preferably is similar to the tools described earlier with respect to theembodiments of FIGS. 1 through 5 and 6, regarding the tilt compensationand other features described in reference to those embodiments.

FIG. 19 shows a housing 181 having an activation switch 182 whichincludes three defined positions: "OFF", "ON", and "ON+DISTANCE". Thus,for the purposes and use of the instrument described earlier relative toFIGS. 1 through 6, the switch 182 is placed in the "ON" position and thetool is used in the manner described above.

When the tool is to be used for acoustic measurement in conjunction witha second component, i.e. the target side device 144 as shown in FIG. 17(and which may take the form shown in FIG. 18), the switch 182 is movedto "ON+DISTANCE". The tool 180 is then positioned at one side of a spaceor room which is to be measured, and a target side device as describedabove is placed at the other side of the space to be measured. The laserbeam 184 is projected, allowing the user to easily position the targetside device such that the laser is directed at the incorporatedphotodetector (158 in FIG. 17). When the target side device sends anacoustic beam, it is received in the microphone 151 as described above,here shown on the front of the laser/plumb combination tool's housing181. Operation is thus similar to that described above.

If the target side device is to be the transponder, rather than thelaser tool 180 being the transponder, then the housing 181 includesadditional components as described above, and the measuring sequence isinitiated by the pulsing of the light beam 184. In either event, theacoustic measuring assembly preferably makes repeated measurements, asdescribed above, as long as the two components are switched to thedistance measuring mode.

In a variation of the combination tool described, the switch 182 in FIG.19 can be replaced with a simple "OFF"/"ON" switch, and thehand-carryable device 180 can include internal switching electronicswhich respond to the receipt of the acoustic signal at themicrophone/receiver 151, to activate the tool to respond with acharacteristic modulation in the laser beam 184. Electronics for thisare not shown but can easily be carried out by one of skill in the art.

The laser tool of the invention can also be provided with means forconnection to a straightedge or a squaring tool, enabling the horizontallaser beam to be projected at a precise angle (e.g. 90°) from a wall orother surface.

Tools described herein are highly versatile and have almost countlessuses in the building trades and other trades. As an instrument forachieving plumb, the tool can be placed alongside a wall or any othermember intended to be vertical. It can be placed on a floor and spottedon a reference mark overhead, e.g. on a roof or ceiling, to locate aprecise position on the floor for passage of pipes or conduits, forexample. In the horizontal beam mode, the tool can be used for levelinga mason's work or for checking level of a floor or any other horizontalmember. It may be used to locate points on the same level, but aconsiderable distance apart, such as in framing or layout work. It canbe used for leveling and as a pointing beam at the same time, toreference straightness of a parallel wall, pipe, structural member, etc.Laid on a broad side, the tool has many uses as a pointing beam withouttilt compensation. It can be set up as desired, as a visible referenceline from which straightness of any member or series of members can bechecked, such as a stud wall. In this mode the beam can be deliberatelydirected at low angles upwardly or downwardly, if desired, since thetilt compensation is deactivated. The acoustic measurement feature maybe used in cooperation with any of the above listed functions, and thetarget side device can be used to locate points by distance, where atape measure would be difficult or impossible to use.

The above described preferred embodiments are intended to illustrate theprinciples of the invention, but not to limit its scope. Otherembodiments and variations to this preferred embodiment will be apparentto those skilled in the art and may be made without departing from thespirit and scope of the invention as defined in the following claims.

I claim:
 1. A laser beam projecting device for plumbing, leveling,alignment and distance measuring, comprising,a hand-carryable housinghaving at least two sides capable of resting stably on a flat surface,the two sides being substantially perpendicular to each other, andincluding two broad sides, laser source means mounted within thehousing, for producing at least one collimated beam of visible laserlight, a laser beam exit window in the housing, positioned in neither oftwo sides nor on said broad sides, beam directing means in the housingfor directing a beam from the laser source means vertically out of thehousing through the exit window when a first side of said two sides isheld generally horizontal, and for directing a beam from the lasersource means horizontally out of the housing through the exit windowwhen a second side of said two sides is held generally horizontal, tiltcompensation means in the housing and associated with the beam directingmeans for correcting for relatively small tilt angles of the housing asit rests with one of said two sides against surfaces not trulyhorizontal or not truly vertical, and for projecting the beam throughthe exit window in substantially true vertical orientation orsubstantially true horizontal orientation despite such relatively smalltilt angles, means associated with the laser beam projecting device fordistance measuring, including:means for characterizing at least onecollimated beam of visible laser light produced at said laser sourcemeans, so that a modulated or pulsed beam is projected from saidhand-carryable housing, and a separate, unconnected component as atarget means with photodetector means for receiving and detecting amodulated or pulsed laser beam projected from the hand-carryablehousing, and with means for projecting an acoustic signal from thetarget means toward the hand-carryable housing, acoustic signal receivermeans in the hand-carryable housing for receiving an acoustic signaltransmitted directly from the target means, without reflection, andmeans coating between the hand-carryable housing and the separate targetmeans, for measuring the time interval between transmission of theacoustic signal at the target means and receipt of the acoustic signalby the receiver means in the hand-carryable housing, with the means forcharacterizing, which causes a modulated or pulsed laser beam to beprojected from the hand-carryable housing toward the photodetector meansof the target means, being part of a response loop for measuring saidtime interval, and with associated means for calculating and displayingthe distance between appropriate points on the hand-carryable housingand the target means in response to said measurement of the timeinterval.
 2. The apparatus of claim 1, wherein:the means for projectingan acoustic signal from the target means comprises an acoustic driverlocated in the target means, serving as the means for transmitting anacoustic signal, the means coacting between the hand-carryable housingand the target means for measuring the time interval comprises:a clockmeans connected to the acoustic drive for timing the interval betweenstart and stop events in which the acoustic signal is transmitted andreceived, manual triggering means in the target means for beginning thedistance measuring sequence by initiating the transmission of theacoustic signal from the target means, and means contained in thehand-carryable housing for triggering a light signal to be emittedtherefrom as a modulated or pulsed laser beam when the acoustic signalis received by the acoustic signal receiver means, whereby upon thetransmission of the light signal, the photodetector indicates thecompletion of a loop wherein the acoustic signal has been received, andthe means for calculating distance and displaying uses the measured timeinterval for calculating and displaying the distance.
 3. The apparatusof claim 1, wherein the distance display means comprises liquid crystaldisplay means on the target means, for displaying a numerical distancescale which is movable relative to the target means as the distancebetween the hand-carryable housing and the target means varies, suchthat the LCD distance scale appears to the user as a tape measure withparticular distance indications fixed relative to the hand-carryablehousing and movable relative to the target means.
 4. An acousticdistance measuring device, comprising,a first component including acharacteristic light signal transmitting means, for being located at afirst position, a second component which is separate from the firstcomponent and which may be placed at a second position, the distance ofwhich from the first position is to be measured, the second componentincluding:a target means with photodetector means for receiving anddetecting a characteristic light signal projected from the firstcomponent, and acoustic means for projecting an acoustic signal from thetarget means toward the first component; acoustic signal receiver meansin the first component for receiving the transmitted acoustic signalfrom the target means, and means coacting between the first componentand the second component, for measuring the time interval betweentransmission of the acoustic signal at the target means and receipt ofthe acoustic signal by the receiver means in the first component, withthe characteristic light signal transmitting means, which projects thecharacteristic light signal from the first component toward thephotodetector means of the target means, being part of a response loopfor measuring said time interval, and with associated means forcalculating and displaying the distance between the first component andthe second component in response to said measurement of the timeinterval.
 5. An acoustic distance measuring device, comprising,a firstcomponent including a characteristic light signal transmitting means,for being located at a first position, a second component which isseparate from the first component and which may be placed at a secondposition, the distance of which from the first position is to bemeasured, the second component including:a target means withphotodetector means for receiving and detecting a characteristic lightsignal projected from the first component, and acoustic means forprojecting an acoustic signal from the target means toward the firstcomponent; acoustic signal receiver means in the first component forreceiving the transmitted acoustic signal from the target means, andmeans coacting between the first component and the second component, forinitiating and carrying out a timing event which is clocked by onacoustic transit time and one optical transit time, without reflection,with associated means for calculating and displaying the distancebetween the first component and the second component in response to saidtiming event.
 6. The apparatus of claim 5, wherein the associated meansfor calculating and displaying the distance includes liquid crystaldisplay means on the target means, for displaying a numerical distancescale which is movable relative to the second component as the distancebetween the hand-carryable housing and the second component varies, suchthat the LCD distance scale appears to the user as a tape measure withparticular distance indications fixed relative to the hand-carryablehousing and movable relative to the target means.
 7. An acousticdistance measuring device, comprising,a first component for beinglocated at a first position, and a second component which is separatefrom the first component and which may be placed at a second position,the distance of which from the first position is to be measured, one wayacoustic transmission means including:acoustic means for projecting anacoustic signal from one of said first and second components to theother, and acoustic signal receiver means for receiving the acousticsignal at the other of said first and second components; light signalmeans for aligning the one way acoustic transmission means, including:acharacteristic light signal transmitting means for transmitting acharacteristic light signal from one of said first and second componentsto the other, and a target means with photodetector means for receivingand detecting the characteristic light signal at the other of said firstand second components; means coacting in said first and secondcomponents for initiating and carrying out a timing event which isclocked by one acoustic transit time and one optical transit time,without reflection, with associated means for calculating and displayingthe distance between the first component and the second component inresponse to said timing event.
 8. The apparatus of claim 7 wherein:thefirst component includes the acoustic signal receiver means forreceiving an acoustic signal, and the characteristic light signaltransmitting means for transmitting a characteristic light signal, andthe second component includes the acoustic means for projecting anacoustic signal from the second component to the first component, andthe target means with photodetector means for receiving and detectingthe characteristic light signal from the first component.
 9. Theapparatus of claim 7, wherein the means coacting in said first andsecond components for initiating and carrying out a timing eventcomprises:a clock means in one of said first and second components fortiming the interval between start and stop events in which one acousticsignal is transmitted and received, triggering means in one of saidfirst and second components for beginning the timing even by initiatingthe start event which includes transmitting one acoustic signal from oneof said first and second components to the other, and means contained inthe other of said first and second components for indicating the stopeven which includes receiving one acoustic signal at the other of saidfirst and second components, whereby the means for calculating distanceand displaying uses the timed interval between start and stop events forcalculating and displaying the distance.
 10. The apparatus of claim 7wherein the means for initiating and carrying out a timing eventincludes a clock means for timing the interval between start and stopevents in which the acoustic signal is transmitted and received, whereinthe start event is communicated by said characteristic light signal andsaid stop event is communicated by said acoustic signal.
 11. Theapparatus of claim 7 wherein the acoustic signal receiver means and theassociated means for calculating and displaying the distance between thefirst component and the second component are at the same one of saidfirst and second components.
 12. The apparatus of claim 7, wherein theassociated means for calculating and displaying the distance includesliquid crystal display means on one of said first and second components,for displaying a numerical distance scale which is movable relative tothe component which includes the liquid crystal display means, as thedistance between the components varies, such that the LCD distance scaleappears to the user as a tape measure with particular distanceindications fixed relative to the other of said first and secondcomponents and movable relative to the component which includes theliquid crystal display means.